There are many circumstances in which it is necessary or desirable to measure the temperature of a hot surface in situ, under conditions in which it is impractical or impossible to provide direct contact by a thermocouple or other form of mechanical probe. For example, such a non-contact technique would beneficially be used to explore and characterize the properties of materials at high elevated temperatures, including in particular the spectral emittance of the material. To achieve utmost accuracy, and consequently the most valuable test data, temperature and emittance must be determined simultaneously, and it is well known in the art that significant difficulties are entailed in achieving that end.
Apparatus and techniques by which temperature measurements can be made remotely, and the significance of emittance considerations thereto, are of course also known in the art. Typical disclosures are found in the following United States patents: Cadwallander et al U.S. Pat. No. 4,506,158, Stein U.S. Pat. No. 4,708,493, Rosenthal U.S. Pat. No. 4,627,008, Berthet et al U.S. Pat. No. 4,799,788, Elleman et al U.S. Pat. No. 4,840,496, Walter U.S. Pat. No. 4,841,150 and Dils et al U.S. Pat. No. 4,845,647. Also of interest in regard to techniques for determining spectral emittance and temperatures by noncontact means, utilizing Fourier-transform infrared (FT-IR) spectroscopy, is the paper entitled "Normal Emittance Measurements By A Transient Temperature Technique," by R. J. Tiernan and J. R. Saunders (J. Appl. Physics 64 (2), Jul. 15, 1988).
Despite the activity in the art indicated by the foregoing, a need remains for a convenient and effective method and apparatus by which the temperature of a hot sample, and its spectral emittance over a desired spectral range at that temperature, can automatically and simultaneously be determined, at high speed and with a high degree of precision. Accordingly, it is the object of the present invention to provide such a method and apparatus.